U.S. patent number 4,820,393 [Application Number 07/048,153] was granted by the patent office on 1989-04-11 for titanium nitride sputter targets.
This patent grant is currently assigned to Tosoh SMD, Inc.. Invention is credited to Teodoro E. Brat, Charles E. Wickersham.
United States Patent |
4,820,393 |
Brat , et al. |
April 11, 1989 |
Titanium nitride sputter targets
Abstract
The present invention provides a sputter target for the
deposition of titanium nitride films. The sputter target has a
target face comprising titanium nitride having a density of at
least 90% of the theoretical density of 100% pure titanium nitride.
The sputter target is prepared by subjecting titanium nitride
powder to hot isostatic pressure.
Inventors: |
Brat; Teodoro E. (Reynoldsburg,
OH), Wickersham; Charles E. (Columbus, OH) |
Assignee: |
Tosoh SMD, Inc. (Grove City,
OH)
|
Family
ID: |
21953014 |
Appl.
No.: |
07/048,153 |
Filed: |
May 11, 1987 |
Current U.S.
Class: |
204/192.15;
204/298.13; 204/192.21; 419/13; 423/411; 501/96.1; 419/49 |
Current CPC
Class: |
C23C
14/3414 (20130101) |
Current International
Class: |
C23C
14/34 (20060101); C23C 014/34 (); C22C 032/00 ();
C01B 021/076 (); C04B 035/58 () |
Field of
Search: |
;204/192.15,192.21,298
;419/13,49 ;423/411 ;501/96 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Nicolet, "Diffusion Barriers in Thin Films", Thin Solid Films, 52,
415 (1978). .
Ting et al, "The Use of Titanium-Based Contact Barrier Layers in
Silicon Technology", Thin Solid Films, 96, 327 (1982). .
Wittmer, "Barrier Layers", Principles and Applications in
Microelectronics, J. Vac. Sci. Technol., A2(2), 273 (1984). .
Sinke et al, "Oxygen in Titanium Nitride Diffusion Barriers", 1985.
.
Sinke et al, "Pre-Annealing of TiN Barriers in Al Metallization of
Silicon", Proc. Mat. Symp., 37, 623 (1985). .
Kanamori, "Investigation of Reactively Sputtered TiN Films for
Diffusion Barriers", Thin Solid Films, 136, 195 (1986). .
Ostling et al, "A Comparative Study of the Diffusion Barrier
Properties of TiN and ZrN", Thin Solid Films, 145, 81
(1986)..
|
Primary Examiner: Valentine; Donald R.
Attorney, Agent or Firm: Biebel, French & Nauman
Claims
What is claimed is:
1. A sputter target for deposition of titanium nitride films having
a target face comprising titanium nitride having a density of at
least 90% of the theoretical density of 100% pure titanium
nitride.
2. The sputter target of claim 1 wherein said titanium nitride has
a density of about 92 to 95% of the theoretical density of 100%
pure titanium nitride.
3. The sputter target of claim 1 wherein said target is prepared by
subjecting titanium nitride powder to hot isostatic pressure.
4. The sputter target of claim 3 wherein said titanium nitride
powder is subjected to hot isostatic pressure at about 1350.degree.
C. and about 20,000 psi for about 4 hours.
5. The sputter target of claim 3 wherein said titanium nitride
powder is subjected to hot isostatic pressure at about 1350.degree.
C. and about 15,000 psi for about 2 hours.
6. A titanium nitride film having a resistivity of about 30 to 70
micron-ohm-centimeters wherein said titanium nitride film is
prepared by providing a titanium nitride target having a density of
at least 90% of the theoretical density of 100% pure titanium
nitride, and sputtering said titanium nitride target to deposit a
titanium nitride film.
7. The titanium nitride film of claim 6 wherein said film is
characterized in that said oxygen is present in the form of
titanium oxynitrides at the surface of said film and as titanium
oxide internally of said film, said titanium oxide being located
along grain boundaries.
8. The titanium nitride film of claim 6 wherein said titanium
nitride film is useful as a diffusion barrier layer in an
integrated circuit.
9. The titanium nitride film of claim 6 wherein said titanium
nitride film is useful as an etch stop layer.
10. A process for depositing a titanium nitride film on a substrate
comprising the steps of
providing a titanium nitride target having a density of at least
90% of the theoretical density of 100% pure titanium nitride;
and
sputtering said target under conditions designed to deposit a
titanium nitride film on said substrate.
11. The process of claim 10 wherein said step of providing said
target includes subjecting a titanium nitride powder to hot
isostatic pressing.
12. A sputter target for deposition of titanium nitride films
having a target face comprising titanium nitride having a density
of at least 90% of the theoretical density of 100% pure titanium
nitride, said titanium nitride comprising about 1,000 to 10,000 ppm
by weight oxygen.
13. The sputtering target of claim 12 wherein said titanium nitride
contains about 5000 to 7000 ppm by weight oxygen.
Description
BACKGROUND OF THE INVENTION
The present invention relates to titanium nitride (TiN) sputter
targets, and more particularly, to TiN sputter targets formed by
hot isostatic pressing; to a method for forming TiN films, and to
TiN films formed by sputtering of the TiN targets.
The integration of a large number of components on a single
integrated circuit chip requires sophisticated interconnections to
minimize signal delays and simultaneously optimize the packing
density. Aluminum has been widely used for contacts and
interconnections in both bipolar and metal-oxide semiconductor
(MOS) integrated circuits. However, the low-temperature
interdiffusion of aluminum and silicon during contact sintering,
passivation, or packaging of the device can result in gain
degradation and increased junction leakage or even shorting of
shallow junction devices. Device reliability can be improved by
interposing a barrier layer between the Al and the Si which reduces
the mass transport in the contact structure during processing or
operation of the device.
TiN films have been proposed as diffusion barrier layers in very
large scale integration (VLSI) metallization schemes and in solar
cell top contacts. A TiN diffusion barrier layer prevents an
undesired reaction between the contact metal such as aluminum and
the substrate material such as silicon, and thus, permits the use
of aluminum in cases where this would otherwise be prohibitive.
Reactive sputtering is a known method for forming TiN films. As
those skilled in the art know, sputtering involves the transport of
a material from a target to a substrate. Ejection of the target
material is accomplished by bombarding the surface of the target
with gas ions accelerated by high voltage. Particles of atomic
dimensions are ejected from the target as a result of momentum
transfer between incident ions and target material ions. These
particles transverse the vacuum chamber and are subsequently
deposited on the substrate in the form of a thin film.
To form a TiN film as part of a layered structure by reactive
sputtering with N.sub.2 for microelectronics applications, the Al
target cannot be present with the Ti target in the sputtering
chamber. If both targets are located in the same chamber, AlN may
form. Therefore, in reactive sputtering a TiN film typically is
formed on a layer such as TiSi.sub.2 in a first sputtering chamber
with a Ti target while an Al layer is formed on the TiN film in a
second sputtering chamber with an Al target. As such, reactive
sputtering is difficult to implement. According to Wittmer,
"Barrier Layers: Principles and Applications in Microelectronics,"
J. Vac. Sci. Technol. A2(2), 273(1984), typical sensitivities for
stoichiometric TiN thin films formed by reactive sputtering range
between about 20 to 70 micron-ohm-cm. While these low resistivity
levels are desirable they are difficult to achieve on an industrial
scale.
Rapid thermal nitridization (RTN) is another method for forming TiN
films. The method is advantageous because the TiN films are formed
in situ. Typically, Ti is sputtered onto a substrate. The Ti film
is then heated to about 1000.degree. C. and N.sub.2 is introduced
so that a TiN film forms. The disadvantages of rapid thermal
nitridization are that the TiN film thickness is difficult to
control, the TiN film may be nonuniform, and hazardous gases such
as NH.sub.3 are present.
Sputtering of a TiN target wherein the target is formed by a hot
press method is another known method for forming a TiN film. The
TiN target is formed by applying heat and pressure simultaneously
to TiN powder at temperatures high enough for sintering of the TiN
powder to occur. TiN targets formed by this method have a density
of about 75% of the theoretical density of 100% pure TiN.
Resistivities for TiN films formed by sputtering of hot pressed
formed TiN targets tends to be about 100 micron-ohm-cm.
A sputtering target and method are desired wherein a layered
structure having a TiN film therein can be formed in one sputter
chamber and the resulting TiN film has a resistivity of less than
about 70 micron-ohm-cm.
SUMMARY OF THE INVENTION
It has been found that TiN films having resistivities on the order
of 30 to 70 micron-ohm-cm are easily obtained by sputtering
deposition using high density TiN targets. These targets are
characterized by a density which is at least about 90% of the
theoretical density of TiN. Typically these targets have a nominal
purity of at least 99.99%. The targets typically are obtained by a
hot isostatic pressing process.
The low resistivity of TiN films produced in accordance with the
present invention is believed to be, at least in part, a function
of the oxygen concentration in the sputtering targets. It is
believed to be desirable for the sputter target to contain about
1,000 to 10,000 ppm (by weight) oxygen, and preferably, 5,000 to
7,000 ppm. Furthermore, the form in which the oxygen is present in
the sputter target is also believed to be important.
Oxygen is known to play an important role in TiN films. As
discussed in Nicolet, "Diffusion Barriers in Thin Films," Thin
Solid Films 52, 415 (1973), some immiscible films do not function
as barrier layers because rapid diffusion along grain boundaries
and other structural defects occur. A remedy is to plug the
diffusion paths with appropriate atoms or molecules, i.e.,
"stuffing" the barrier. When these paths are plugged by suitable
impurities, the stuffed barrier can successfully withstand the heat
treatment.
For example, when impurities such as oxygen stuff a TiN diffusion
barrier layer, the oxygen is probably absorbed along the grain
boundaries of the TiN diffusion barrier layer, and thus, prohibits
Al from diffusing into the layer. Oxygen concentration in the TiN
diffusion barrier layer may be increased by exposing the TiN
diffusion barrier layer to air before Al deposition. Also, Al.sub.2
O.sub.3 may be formed upon annealing which is known to be very
effective against Al diffusion.
Although further work is required to confirm the observation, TiN
films produced in accordance with the invention appear to contain a
thin coating of titanium oxynitride, but the oxygen contained
internally of the nitride is believed to be distributed along grain
boundaries as titanium oxide. In the grain boundaries, the oxide
effectively closes the diffusion pathway, and in so doing,
contributes to the barrier properties of the film without severely
compromising resistivity.
One manifestation of the present invention is a sputter target for
depositing TiN film comprising a stage holding TiN having a density
of at least 90% of the theoretical density of 100% pure TiN.
Another manifestation of the present invention is a process for
depositing TiN films which comprises the steps of:
providing a TiN target having a density of at least 90% of the
theoretical density of 100% pure TiN, and
sputtering said target under conditions designed to deposit a TiN
film on a substrate.
Still another manifestation of the present invention is a TiN film
produced by the aforesaid process and more particularly, an
integrated circuit having a TiN film as a barrier layer.
Other objects and advantages of the present invention will become
apparent from the following description and appended claims.
DETAILED DESCRIPTION OF THE INVENTION
The TiN sputter target of the present invention is characterized by
a density of at least 90% of theoretical, and most typically, about
92 to 95% of theoretical.
While other processes may be used to form the sputter target of the
present invention, it is preferably formed by a process known as
hot isostatic processing. In a typical process, a 1 micron TiN
powder is placed in a steel hot isostatic pressing can. The powder
is vibrated and compacted and the can is sealed. The can is
evacuated to a pressure of about 10 to 100 microns and placed in a
hot isostatic press.
Two sets of pressing conditions have been evaluated and found to be
essentially equivalent. In one set, the press is operated at
1350.degree. C. at 20,000 psi for 4 hours to produce the target. In
the other set, the press is operated at 1350.degree. C. and 15,000
psi for 2 hours.
After pressing, the can is removed from the press and the steel can
is removed from the TiN target by machining. The TiN cake is cut
into a shape such as a disc having a diameter of about 5 cm which
can be placed in or bonded to a support in preparation for
sputtering.
Both procedures yield a gold colored sputtering target having a
density of 92-95% of theoretical target. X-ray diffraction
indicates that the target material matches exactly a simulated
stoichiometric TiN pattern. A typical elemental analysis for the
impurities in a sputter target in accordance with the present
invention is shown in Table 1.
TABLE 1 ______________________________________ ELEM. Si Al Ca Co Cr
Cu Fe Mg Mn ______________________________________ PPM ND ND 11 5 6
13 52 ND 13 ______________________________________ ELEM. Ni Mo NA K
Li U TH ______________________________________ PPM 15 5 1.8 ND ND
0.010 0.027 ______________________________________
Sputtering involves transporting material from the TiN target to a
substrate. The ejection of the TiN target material is accomplished
by bombarding the surface of the TiN target with gas ions
accelerated by high voltage. Typically, ultra high purity argon is
used. Molecular size particles are ejected from the TiN target as a
result of momentum transfer between incident ions and atoms of the
TiN target material. These particles traverse the vacuum chamber
and are subsequently deposited on the substrate as a thin film.
Typically, the TiN target is water cooled.
A magnetron sputtering system is particularly useful in the present
invention. Useful sputtering systems are commercially available.
Typically, the TiN deposition rate is high and ranges from about 35
to 40 angstroms/sec. The TiN can be deposited on the substrate to a
desired thickness. Because conductivity is an intrinsic property,
i.e., a property which exists independent of dimensions, the film
thickness can be varied as desired to meet a given application.
Typically, the thickness of the TiN films ranges from about 100 to
300 nm.
Table 2 contains useful sputtering conditions and the properties of
the resulting TiN films. The deposition rate was about 38
angstrom/sec and the TiN film thickness was about 180 nm. The
substrate temperature is in .degree.C. while the bias in in
direct-current volts.
TABLE 2
__________________________________________________________________________
SPUTTERING CONDITIONS Substrate Temp. Bias N.sub.2 Spacing
STOICHIOMETRY RESISTIVITY RS Sample # [.degree.C.] VDC [SCC]
[angstroms] Ti N O Ti/N N/O [ohms/area] [micro-ohm-cm]
__________________________________________________________________________
1 -- -- -- 2.47 2.140 0.462 0.473 0.065 0.98 7.3 2.67 47 2 -- 550
-- 2.473 2.135 0.475 0.480 0.045 0.99 10.7 2.66 47 3 -- -- 100
2.479 2.154 0.460 0.485 0.055 0.95 8.8 3.65 65 4 -- 550 100 2.486
2.154 0.478 0.475 0.047 1.00 10.1 3.64 65 5 400 -- -- 2.467 2.130
0.475 0.465 0.060 1.02 7.8 2.21 39 6 400 750 -- 2.465 2.130 0.470
0.470 0.060 1.00 7.8 2.20 38 7 400 700 100 2.467 2.133 0.450 0.492
0.058 0.91 8.4 2.88 51
__________________________________________________________________________
The stoichimetry in atomic % of Table 2 was determined by
Rutherford Backscattering Spectrometry (RBS). As those skilled in
the art know, RBS is a nondestructive analytical technique which
provides an in-depth profile of the elements constituting a thin
film system. As indicated, Ti, N, and O were present as principal
components of the films. No argon gas was detected in the films
within the sensitivity of the RBS technique. Ti to N atomic ratios
in the films varied from 0.9 to 1.02 according to RBS results. It
is evident that stoichiometry is strongly dependent on the
sputtering conditions as shown in Table 2.
The resistivities as shown in Table 2 range from 38 to 65
micron-ohm-centimeters. Acceptable resistivities range from about
30 to 70-micron-ohm-centimeters. As shown in Table 2, heating the
substrate resulted in films having resistivities from 38 to 51
micron-ohm-centimeters. Bias apparently does not affect the
resistivity of the film. The film samples were gold in color.
The depth profile composition of Table 3 below was determined by
Electron Spectroscopy for Chemical Analysis (ESCA). As those
skilled in the art know, ESCA is a form of electron spectroscopy in
which a sample is irradiated with a beam of monochromatic x-rays
and the energies of the resulting photoelectrons are measured. The
sputtering rate was 20 angstroms/minute and the accuracy of the
results is + or -10%. The binding energies indicated that Ti and N
are present in compound form. The ESCA profile analysis shows that
the film surface comprises titanium oxynitrides (Ti.sub.x O.sub.y
N) while the film interior comprises TiN.
TABLE 3 ______________________________________ SPUTTERING ELEMENT %
TIME [Min] Ti N O C Si ______________________________________
SAMPLE A 9 51.08 44.12 3.12 1.69 0.27 48 53.08 44.25 1.92 0.77 0.00
99 53.26 43.75 1.92 1.07 0.00 SAMPLE B 9 52.99 43.61 2.74 0.67 0.00
48 52.62 43.76 2.91 0.62 0.00 99 54.45 43.06 1.55 0.94 0.00
______________________________________
X-ray diffraction was used to determine the film structure. TiN has
a face-centered cubic structure (FCC) comparable to sodium chloride
(NaCl). TiO is isomorphic with TiN. X-ray diffraction indicated
that the TiN target material matches exactly a simulated
stoichiometric TiN pattern while the deposited TiN film shows a
shift in the crystallographic plane spacing of the (111) and (200)
reflections.
Table 4 shows a comparison of the properties of TiN films formed
by: (1) the present invention--sputtering of a TiN target formed by
hot isostatic pressing, (2) reactive sputtering of a Ti target, and
(3) rapid thermal nitridization (RTN) of Ti/Si (100) in
N.sub.2.
TABLE 4 ______________________________________ (1) TiN (2) Reactive
Target Sputtered (3) RTN ______________________________________
RESISTIVITY 40 160 100 [micron-ohm-cm] DEPOSITION RATE 40 10 --
[angstrom/sec] FILM THICKNESS 1800 1000 1000 [angstroms] DIFFUSION
BARRIER 560 500 500 TEMPERATURE Al/TiN/TiSi.sub.2 /Si (100)
[.degree.C.-60 min.] FILM THICKNESS At Least At Least At Least (NO
PEELING) 4000 2000 2000 [angstroms]
______________________________________
As Table 4 shows, a TiN film formed by the present invention
yielded the lowest resistivity, i.e., 40 micron-ohm-cm and the
fastest deposition rate, i.e., 40 angstroms/sec.
Each TiN film was formed as a diffusion barrier in a
Al/TiN/TiSi.sub.2 /Si(100) structure to determine thermal
stability. The diffusion barrier temperature is the highest
temperature at which the layered structure remained thermally
stable for 60 minutes. With an Al/TiN/TiSi.sub.2 /Si(100) layered
structure, the Al reacts with the TiN to form AlN and Al.sub.3 Ti.
Eventually the interdiffusion of Al and Si can result in grain
degradation and increased junction leakage or even shorting of
shallow junction devices. The TiN film formed by the present
invention yielded, at 60 minutes, the highest diffusion barrier
temperature, i.e., 560.degree. C.
Based on the foregoing discussion, the TiN films of the present
invention are particularly useful in integrated circuits as
diffusion barrier layers in layered structures such as Al/TiN/Si
and Al/TiN/TiSi.sub.2 /Si. The TiN films have also been studies for
use as local interconnects, contacts between metals and silicides,
blocking Ti-Pt reaction, highly stable solar cells, and as a
sticking layer for CVD tungsten. The TiN films can also be used as
etch stop layers for reactive ion etching.
Having described the invention in detail and by reference to
preferred embodiments thereof, it will be apparent that
modifications and variations are possible without departing from
the scope of the invention defined in the appended claims.
* * * * *